Whole human blood includes predominantly three types of specialized cells: red blood cells, white blood cells, and platelets. These cells are suspended in a complex aqueous solution of proteins and other chemicals called plasma. Although in the past blood transfusions have used whole blood, the current trend is to transfuse only those blood components required by a particular patient. This approach preserves the available blood supply and in many cases is better for the patient, since the patient is not exposed to unneeded blood components. Storage lifetimes can also be increased by packaging the individual blood products separately.
The blood components needed for the transfusion are taken from a donor by a process called apheresis in which the desired one, or more, specific components of the whole blood are separated and harvested by a blood-processing machine. The remaining components are returned to the donor. (As used herein, the term "donor" connotes anyone from whom blood is drawn for collection or processing, and can include volunteer donors or medical patients to whom blood collected components are returned.) Typically, an apheresis apparatus has several peristaltic pumps and a number of valves for controlling the direction and duration of blood flow from the donor and through a recirculating separation process. The device provides a separation chamber, having input and output ports, for separating blood components according to their densities. The output port of the separation chamber is in fluid communication with one or more blood component containers that receive the separated blood components. The output put port may be in further fluid communication with the input port through a recirculation pump in order to recirculate less dense blood components and/or plasma. A phlebotomy needle for withdrawing whole blood from the donor is in fluid communication with the apheresis apparatus and an anticoagulant container.
In operation, a "blood collection cycle" or "draw process" begins with the withdrawal, through the phlebotomy needle, of whole blood from a donor. The whole blood is anticoagulated by mixing with anticoagulant drawn from the anticoagulant container, and the anticoagulated whole blood enters the separation chamber through the input port. During the draw process, a separation process separates lower-density components from higher-density components in the separation chamber. The less-dense component(s) is (e.g., plasma, platelets, and white blood cells) are displaced through the output port into the blood component containers. The separation process is then terminated, and the higher-density components (e.g., red blood cells or "RBC") remaining in the separation chamber are diluted with diluent and returned to the donor, or collected as an RBC product. More specifically, a diluent solution is stored in a diluent container in selective fluid communication with the flow path between the input port of the separation chamber and the phlebotomy needle, and the higher-density components remaining in the chamber are drawn out through the inlet port, mixed with diluent from the diluent container and returned to the donor via the phlebotomy needle. The entire apheresis procedure may be repeated with additional draw processes, wherein whole blood is again drawn from the donor and combined with anticoagulant from the anticoagulant container, followed by additional separation processes.
The apheresis procedure described above is merely exemplary. A number of different apheresis procedures are known in the art, and specific apheresis procedures have developed in response to the demand for specific blood components. In particular, the demand for platelet concentrates with low contamination of white blood cells ("WBC"), such as lymphocytes, has grown rapidly with advances in medical science and cancer therapy. Consequently, a number of procedures are now directed toward optimizing the collection of pure platelet concentrate (see for example U.S. Pat. Nos. 5,494,592 and 4,416,654). A blood drawing process may also be used in non-apheresis procedures such as whole blood collection.
While efficient and straightforwardly practiced, these procedures nonetheless exhibit limitations. In particular, a low donor blood flow rate through the phlebotomy needle often prolongs the time for the draw process. For this reason, a donor should periodically squeeze his hand during the draw process in order to maintain adequate venous pressure at the phlebotomy needle site. Failure of the donor to squeeze his hand will frequently result in reduced blood flow and consequent reduction in pump speed, thus increasing the duration of the procedure and negatively affecting the collection process. If the blood flow rate consistently drops below that required by the collection device, the procedure may be terminated in order to prevent health risk to the donor. To effectuate this safety feature, blood collection systems typically include a donor pressure monitor that senses changes in the line pressure and a control system that slows or stops the peristaltic collection pumps in response to decreasing pressure. The resulting conditions are known as "Low Flow" or "No Flow."
In order to avoid Low Flow/No Flow conditions, a donor is typically provided with a hand-held gripping device or hand gripper which the donor should be reminded to squeeze during the draw process. Some blood drawing apparatus also include a visual indicator which responds to decreasing blood flow rates and alerts the donor to squeeze the hand gripper. However, due to lack of proper instruction and/or lack of donor attention to the alert signal, pressure-related interruptions to blood collection continue to prolong blood drawing procedures.
Accordingly, there is a continuing need for a device to reduce procedure times in blood drawing by interacting with the donor in a manner that assures adequate venous pressure for uninterrupted blood flow.